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The mechanical behaviour of geomaterials is complex and, as a consequence, material models form an important part of any numerical analysis in geotechnical engineering. There are so many constitutive models already available that an external observer might well question whether further constitutive models should be developed or, rather, existing models should somehow be compared and evaluated. There is no consensus within the geotechnical engineering community in addressing this question. Practising engineers are at the mercy of the model developers as they try to discover which model might be suitable for which purpose. The developers themselves are rarely impartial in their evaluation: they will typically extol the virtues of their own modelling framework while at the same time recommending further enhancement.However, there is, in our opinion, a logical way to respond to the question. The evaluation of constitutive models should be in the hands of researchers and practitioners who wish to make use of the models for solving practical problems; leaving the developers to respond to their objective conclusions and use them for further improvement of the models. Unfortunately, the current state of constitutive modelling does not permit this line of thinking to be followed. Users of constitutive models generally have neither the time nor the expertise to implement the models into finite element (FE) codes by themselves and therefore their choice of models remains confined to the few (often primitive) models that happen to be already available in commercial FE codes or, perhaps, they may have access only to particular models that are being developed at their own research institutions. *